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1988 (1)
1Author    Y. Shiraiwa, K. P. Bader, G. H. SchmidRequires cookie*
 Title    Mass Spectrometry Analysis of Oxygen Gas Exchange in High-and LOW-C0 2 Cells of Chlorella vulgaris  
 Abstract    Oxygen gas exchange was monitored in the unicellular green alga Chlorella vulgaris 211 — 11 h by means of a mass spectrometer equipped with a special membrane gas-inlet-system and a photosynthetic reaction vessel. C02-dependent I8 02-uptake as well as ,6 02-evolution were ana-lyzed in both High-and Low-C02 cells. In High-C02 cells, the 18 Oruptake in the light (UL) decreased by 65% upon addition of 3 mM NaHC03, while l6 02-evolution (E) was increased approx. 1.8 times by the same treatment. 18 02-uptake in the dark (UD) was not affected by the addition of external inorganic carbon (Ci). The addition of 3.3 mM NaHCO, also affected UL and E in Low C02-cells, however, to a minor extent. UL under C02-saturating conditions was light intensity-independent up to 2 klux and 1.2 klux in High-and Low-C02 cells, respectively. Above these light intensities UL increased approx. 4-fold in High-and approx. 6-fold in Low-C02 cells. Under C02-limiting conditions, however, UL increased in High-CO: cells even under very low light intensities, showing that photorespiratory oxygen uptake occurred even in the near vicinity of the light compensation point. Under C02-saturating and strong light conditions UL represented almost half of E in Low-C02 cells and about 30% of E in High-C02 cells. In Low-C02 cells addition of ethoxyzolamide (EZA), an inhibitor of carbonic anhydrase, enhanced UL and suppressed E and NET under C02-limiting conditions, whereas the compound had only a minor effect on High-C02 cells. DCMU (3 |XM) strongly inhibited E and UL under C02-saturating conditions, with the remain-ing UL being smaller than UD. KCN (1 mM) and SHAM (1.5 mM) added to DCMU-treated Low-C02 cells suppressed UL by approx. 50%. The resulting value corresponded to half of UD. KCN also inhibited E under CÓ2-saturating conditions, with UL being strongly enhanced showing a maximal uptake at 0.4 mM KCN. Under these conditions NET was nearly zero. The effect seems to be due to an inhibition of RubisCO and an enhancement of Mehler reactions. At 0.7 mM KCN, DCMU entirely inhibited UL, but oxygen uptake appeared increased after turning the light off. This uptake corresponded to approx. 60% of UD. Whereas KCN and SHAM inhibited approx. 70% of UD, only 16% of UL was suppressed. These results suggest that the contribution of mitochondrial respiration to UL was négligeable, since UL seemed to be suppressed in the light under C02-saturated conditions. Iodoacetamide, which is an inhibitor of the Calvin cycle and thereby diverts carbon into the respiratory pathway, inhibited E and NET under C02-saturating conditions, but did not affect UL. This result also shows that UL is not due to mitochondrial respiration. A hydroxylamine derivative [20, 21] which changes the ratio of the RuBP carboxyla-tion to oxygenation activity in tobacco leaves did not affect this ratio in Chlorella. 
  Reference    Z. Naturforsch. 43c, 709—716 (1988); received May 24 1988 
  Published    1988 
  Keywords    Chlorella, Oxygen Gas Exchange, Carbonic Anhydrase, Mass Spectrometry 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0709.pdf 
 Identifier    ZNC-1988-43c-0709 
 Volume    43